Usually, in the production line of a factory, many industrial robots for automatically performing a welding operation, an attaching operation of parts, a conveying operation or the like are employed. Prescribed operations are previously taught to the industrial robots by exclusive teach pendants and the robots perform various kinds of operations by reproducing the contents of teaching. The teach pendant is also ordinarily referred to as a teach device. A similar teach pendant is used for teaching (program) working procedures of various kinds of machine tools, NC machine tools, etc.
A teaching operator ordinarily holds such a teach pendant by one hand and performs operations for input keys by the other hand to teach the machines. In this case, the industrial robots or the NC machine tools as objects to be taught (refer generally them to as a device, hereinafter) sequentially carry out operations respectively for steps in accordance with a teaching operation. For example, a driving operation of a motor, a swing operation of an arm, an operation for turning on a work head (for instance, a welding gun) or the like are performed. At this time, the device may sometimes make an operation different from that intended by the teaching operator owing to a mistake in teaching operation or the defects of the parts of the device. In such a case, to avoid a danger to operators in the vicinity of the device including the teaching operator and prevent the device and peripheral devices from being broken, a safety system of the device needs to be constructed so that the teaching operation is immediately inhibited or the device is quickly stopped.
Accordingly, in the usual teach pendant, at the time of the operation that is not intended by the teaching operator as described above, an enable switch is employed so that the teaching operation is assuredly inhibited and the device is immediately stopped. Further, the enable switch is arranged at both sides of the teach pendant for the whip hand of the teaching operator or for the purpose of improving the efficiency of the teaching operation, and proposed and used so as to be operated by both the hands.
Since muscles wither due to a surprise or an electric shock when a danger impends to a human being, for instance, the hands are held tightly. Therefore, for the enable switch, a three-position switch of a momentary type is used. A state that the teach pendant is not gripped is located at a below-described first operation.
To obtain a permitting state that the operation of the device is permitted and an inhibiting state that the operation of the device is inhibited, a below-described enable contact signal of the three-position switch is outputted to the device. An enable contact is constructed so as to open to have the inhibiting state that the operation of the device is inhibited when a pressing-down stroke is operated to be located in the first operating position smaller than a prescribed range and to be located in a third operating position larger than the prescribed range, and so as to close to have the permitting state that the operation of the device is permitted when the pressing-down stroke is operated to be located in a second position within the prescribed range. Further, when the enable contact is placed at the third operating position once, in the second operating position where the pressing-down stroke is mitigated until the enable contact is placed at the first operating position, the enable contact is not closed to maintain the inhibiting state that the operation of the device is inhibited.
For instance, the teaching operator may hold the teach pendant by a left hand and carries out the teaching operation by a right hand, or vice versa. Further, in the teaching operation for a long time, by considering the fatigue of fingers or hands, the three-position switches are arranged at two positions including a part which left fingers touch and a part which right fingers touch so that the teach pendant can be arbitrarily shifted from one hand to the other hand. The two three-position switches can respectively permit the device to be operated.
Further, the three-position switches are desirably constructed so that when one three-position switch is located at the third operating position, the inhibiting state that the operation of the device is inhibited is established until both the three-position switches are placed at the first operating positions, as proposed in Patent Document 1 and patent Document 2.
Patent Document 1: JP-A-2002-355781
Patent Document 2: JP-A-2002-83522
In an embodiment disclosed in the Patent Document 1, when one three-position switch is gripped and held at the second operating position, an enable contact is closed to obtain a permitting state that the operation of a device is permitted. Then, when the other three-position switch is operated to be located at the second operating position, the enable contact is opened to obtain an inhibiting state that the operation of the device is inhibited. That is, only when one three-position switch is placed at the second operating position, the permitting state for permitting the operation of the device is obtained.
In an embodiment disclosed in the Patent document 2, when one three-position switch is held at the second operating position, an enable contact is closed to obtain a permitting state that the operation of a device is permitted. Then, even when the other three-position switch is located at the second operating position, the permitting state for permitting the operation of the device is maintained.
Ordinarily, the teaching operator grips the teach pendant by one hand and carries out an operation for pressing down input keys by the other hand to perform the teaching operation. Generally, in the teaching operation for a long time, the operator has a chance to arbitrarily shift the teach pendant from one hand to the other hand due to the fatigue of fingers or hands. An operating method during shifting the teach pendant from one hand to the other hand includes two methods of (1) that both the three-position switches are opened once to obtain the first operating positions and the other three-position switch is operated to be located at the second operating position, or (2) that both the three-position switches are placed at the second operating positions and the other switch is opened to be located at the first operating position.